1. Field of the Invention
This invention relates to an endoscope apparatus used for observation and recording of the interior of a section unobservable from the exterior, and more particularly to an endoscope apparatus provided with a solid state image pickup device.
2. Description of the Prior Art
In general, endoscopes, also called fiber scopes, are used to observe the interiors of body cavities or equipment and record images of the interiors. An end section of the fiber scope inserted into the interior to be observed includes an image forming optical system for forming an image of an object, one end of an optical fiber bundle called an image guide for transmitting the optical image created by the image forming optical system to the other end of the image guide, and one end of an optical fiber bundle called a light guide for illuminating the object. The optical image transmitted through the image guide is then enlarged by a loupe to facilitate observation, recorded on a photographic film or displayed by a CRT.
Recently, advances in semiconductor technology have led to the wide use of self-scanning type solid state image pickup devices, such as charge coupled devices (CCDs), and television cameras using solid state image pickup devices of this type have been put to practical use. The solid state image pickup devices of this type have an advantage over the image pickup tubes conventionally employed in television cameras, such as vidicons, in that they are smaller in size and lighter in weight. Under the above circumstances, it has been proposed in Japanese Unexamined Patent Publication Nos. 51(1976)-65962 and 49(1975)-114940 to incorporate a self-scanning type solid state image pickup device directly in in the above-described end section of an endoscope and convert the image of an object formed by the image forming optical system into an electric signal to display a television image on an image receiver (CRT display unit).
In general, to obtain a color television image on a CRT display unit, one of the image pickup systems described below will be employed. In the first and basic system, an image of an object formed by an image forming optical system is color-separated to red (R), green (G) and blue (B) color images, and three discrete solid state image pickup devices corresponding to the three primary colors are used. In the second system, only one solid state image pickup device is used, and red, green and blue primary-color filters are arranged in a mosaic form for respective picture elements of the solid state image pickup device to achieve multiplexing of the image pickup surface. In the third system, red, green and blue primary-color filters are rotated at a predetermined speed in front of a light source. The light source emits light to the illuminating member of the endoscope, i.e. the above-mentioned optical fiber bundle called a light guide, and the red, green and blue primary-color components of the image are picked up in a plane-sequential manner from a single solid image pickup device. However, these conventional systems present very real problems when used for endoscopes. Namely, the first system cannot be incorporated into a small and thin end section of an endoscope, although it is the most fundamental configuration and can provide good television images. If the first system is incorporated in the end section of an endoscope, the end section becomes large and the application range of the endoscope is limited. The second system can be incorporated in a small end section of an endoscope. However, in the second system, since the image pickup surface of the solid state image pickup device is color-separated by red, green and blue primary-color filters arranged in a mosaic form, the number of the picture elements for the green component that determines the resolving power is reduced, resulting in a drop in the resolving power. Particularly, when the end section of the endoscope is made small, it is difficult to use a solid state image pickup device having many picture elements. In this case, therefore, a reduction in the resolving power presents a very real problem. In the third system, since the three primary color components of the image are sequentially picked up by using a single solid state image pickup device in a plane-sequential mode, a problem concerning the timing of registration of the three primary color image arises for an object moving at a relatively high speed, resulting in deterioration of the image quality.